In the field of semiconductor material processing, semiconductor material processing apparatuses including vacuum processing chambers are used, for example for etching and chemical vapor deposition (CVD) of various materials on substrates, and for resist stripping. Some of these processes utilize corrosive and erosive process gases and plasma in such processing chambers. It is desirable to minimize particle and/or metal contamination of substrates processed in the chambers. Accordingly, it is desirable that plasma-exposed components of such apparatuses be resistant to corrosion when exposed to such gases and plasma.
Aluminum alloys such as Al6061-T6 and Al5052 have been using as plasma processing chamber materials since the 1980s. Since many aggressive and reactive gases such as Cl2, HCl, HBr, SF6, and NF3 are used in plasma processing chambers, aluminum alloys have to undergo surface modification to form a coating which can provide higher corrosion resistance and longer part lifetimes. Among aluminum alloys, both 6XXX and 5XXX series of aluminum alloys are attractive aluminum substrates. For example, Al 5XXX series alloys have moderate to high strength, good weldability, and high corrosion resistance of anodic film. Al6XXX series alloys are heat treatable, good formability, weldability, machinability, and high corrosion resistance of anodic film. For Al5XXX alloys, magnesium (Mg) is the principal alloying element. For Al 6XXX alloys, magnesium and silicon are the principal alloying elements. These aluminum alloys may also contain other alloying elements such as Fe, Cu, Zn, and Mn.
With semiconductor wafer etch feature size shrinkage to 28 nm, 20 nm and even 14 nm, metal contamination reduction in such aluminum alloys becomes more and more critical. For example, it is desirable to reduce Fe contamination levels from about 1×1010 atoms/cm2 down to about 1×108 atoms/cm2. It is also desirable to reduce other metal contaminants such as Al, Mn, Cr, Cu, and Zn. Among the metal contaminants, Fe reduction is believed to be most critical and Fe contamination may come from different sources in the plasma processing chamber such as any stainless steels used in the chamber. The Fe from aluminum alloy 6061-T6 itself is another major source of contamination in the plasma processing chamber.
Therefore, it is desirable to minimize metal contamination on aluminum substrates used in plasma processing chambers.